A positive electrode active material powder is used for a nonaqueous electrolyte secondary battery such as a lithium secondary battery. The nonaqueous electrolyte secondary battery is already practically used as a power source for cellular phones and laptop computers, and the attempts are made to apply the nonaqueous electrolyte secondary battery for middle-sized and large-sized applications such as automobiles and electric power storage units.
Japanese Unexamined Patent Publication No. 6-325791 expressly discloses, as a conventional positive electrode active material powder, a powder having an average primary particle diameter of 0.54 μm to 2.02 μm and an average secondary particle diameter of 3.6 μm to 10 μm, and Japanese Unexamined Patent Publication No. 2005-141983 expressly discloses a powder having an average primary particle diameter of 0.17 μm to 0.7 μm and a median diameter of secondary particles of 6 to 12 μm, respectively.